Heart valve replacement may be indicated when there is a narrowing of the native heart valve, commonly referred to as stenosis, or when the native valve leaks or regurgitates, such as when the leaflets are calcified. In one therapeutic solution, the native valve may be excised and replaced with either a biologic or a mechanical valve. Prosthetic valves attach to the patient's fibrous heart valve annulus, with or without the leaflets being present.
Two primary types of heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a ball and cage arrangement or a pivoting mechanical closure supported by a base structure to provide unidirectional blood flow, such as shown in U.S. Pat. No. 6,645,244 to Shu, et al. The other is a tissue-type or “bioprosthetic” valve having flexible leaflets supported by a base structure and projecting into the flow stream that function much like those of a natural human heart valve and imitate their natural action to coapt against each other and ensure one-way blood flow. In tissue-type valves, a whole xenograft valve (e.g., porcine) with leaflets or a plurality of individual xenograft leaflets (e.g., bovine pericardium) provide the fluid occluding surfaces. Synthetic leaflets have been proposed, and thus the term “flexible leaflet valve” refers to both natural and artificial “tissue-type” valves. Two or more flexible leaflets are mounted within a peripheral support structure that usually includes posts or commissures extending in the outflow direction to mimic natural fibrous commissures in the native annulus. For example, the CARPENTIER-EDWARDS Porcine Heart Valve and PERIMOUNT Pericardial Heart Valve available from Edwards Lifesciences of Irvine, Calif. each include a peripheral support structure with an undulating wireform and surrounding stent.
Certain support components of prosthetic valves are assembled with one or more biocompatible fabric (e.g., Dacron, polyethylene terepthalate) coverings, and a fabric-covered sewing ring is typically provided on the inflow end of the valve. The fabric coverings provide anchoring surfaces for sutures to hold the flexible leaflets and sewing ring to the peripheral support structure. In a typical assembly procedure, a technician manually holds a tubular fabric around the support component, and the sewing occurs in two stages; first, intermittent stitches are placed to secure the fabric in its gross position around the stent, and then a closely-spaced line of stitches is applied to complete the seam, still with some manual tension on the fabric. The holding and stitching operation is entirely manual and done under a magnifier, which makes it quite labor-intensive and time-consuming. The work requires the passage of needle and thread through multiple layers of fabric and sometimes biological tissue, and requires considerable effort and precision. Needless to say, repetitive stress injuries can occur which is painful to the worker and indirectly increases the cost of making the valve. The number one factor for injury and lost time in this field is the intricacy of manual sewing.
Rigorous quality control in the manufacture of heart valves further increases the difficulty of the task because the fabric must be tightly fitted around the support component and every stitch carefully placed for consistency. Operator-to-operator variability in sewing technique, stitch tension, stitch pitch, and other variables can result in subtly different construction and end product quality. A typical tissue-based heart valve requires 6-8 hours of manual construction, and the manual sewing procedure represents a substantial portion of the cost of the entire valve fabrication process. Moreover, training of heart valve assembly operators to become proficient in sewing can take upwards of 12-14 months.
Automation is usually an option in manufacturing processes, but is not a factor in the production of prosthetic heart valves because of their odd shapes and strict quality control. Indeed, manual sewing has the advantage of the operator being able to continually check the quality and success of their sewing. Mistakes can be corrected on the spot. Although automation speeds the process up, and is quite repeatable and reliable, it is not infallible and the careful manual visual inspection of each stitch would be lost. In general, because most of the steps in assembling prosthetic heart valves are specialized tasks performed in a clean room to produce an implant that must be highly sterile and perfectly assembled, robotics and other such ubiquitous tools of automation are not easily adapted.
There is thus a need for an improved method for assembling flexible heart valves that reduces the assembly time and the instances of injury to the assembly-line workers.